A typical inkjet print head contains an ink reservoir, in which the ink completely surrounds an internal heater array that forms a print head circuit. The heater array typically contains multiple heating elements such as thin or thick film resistors, diodes, and/or transistors. The heating elements are arranged in a regular pattern for heating the ink to the boiling point. Each heating element in the heater array can be individually or multiply selected and energized in conjunction with other heating elements to heat the ink in various desired patterns, such as alpha-numeric characters. The boiled ink above the selected heating elements shoots through corresponding apertures in the inkjet print head immediately above the heater array. The ink jet droplets are propelled onto printer paper, or other printing media, where they are recorded in the desired pattern.
FIG. 1 illustrates a typical heater array, or print head circuit, 100 in an inkjet printer. The print head circuit includes multiple row select lines A1 through AM, wherein select lines A1 through A3 are shown, and multiple column select lines B1 through BN, wherein select lines B1 through B3 are shown. Spanning the row and column select lines are heating elements represented as resistors R11 through RMN, wherein resistors R11 through R33 are shown, in series with switching elements that are typically metal oxide semiconductor field effect transistors (MOSFETs) M11 through MMN, wherein MOSFETs M11 through M33 are shown. The column select lines B1 through BN are coupled to and selectively energize or fire up the gates of the MOSFETs. No heating current actually flows through the column select lines. The row select lines A1 through AM are coupled to and selectively provide heating current to the rows of resistors R11 through R1N, R21 through R2N, R31 through R3N, etc. Thus, individual resistors may be selected for high resolution printing by energizing the corresponding row and column select lines. A specific resistor is selected and energized by, for example, by energizing or firing up a row of resistors with a corresponding row select line and energizing or firing up a column select line to energize the gate of the specific resistor (and the gates of other MOSFETs in the column of the specific resistor).
One problem with the print head circuit 100 is the expensive integrated circuit process and design technology that is conventionally used to fabricate such a circuit, which requires individual control of resistors. For example, with the present MOS technology, a minimum of seven semiconductor masks must be used to fabricate the MOSFETs M11 through MMN, which prolongs and increases the cost of the fabrication process for the print head circuit 100.
Accordingly, there is a desire for a low-cost design of a print head circuit that may be manufactured using a shorter and simpler semiconductor fabrication process for applications which desire fast print speed at lower print quality, such as transactional printing, etc.